In clinical practice, evaluation of the extent to which a patient's eyeball, or bulbus oculi, is red or some other color is often indicative of a condition of the bulbus oculi. Although red is generally the most relevant color, colors other than red can be relevant. Also, the extent of “redness” of an exposed portion of a tarsal area, i.e., the part of the eyelid which is normally in contact with the eyeball, is often indicative of a condition of the eyeball or the patient. A clinician is often concerned with determining the extent of redness of the bulbus oculi or the tarsal area, although redness is only one possible indicator. The term clinician, as used herein, means an optometrist, an ophthalmologist, or a general medical practitioner.
In particular, the clinician typically assesses the redness of an exposed portion of the bulbus oculi or an exposed portion of the tarsal area, as the case may be, over a period of time, during treatment of the patient's condition. Detecting variations (i.e., decrease or increase) in redness of the bulbus oculi or the tarsal area during treatment can be helpful in assessing changes in a patient's condition. For example, a gradual increase in redness of the bulbus oculi (or the tarsal area), or no change in redness, may suggest to the clinician that changes in treatment are warranted.
In certain circumstances, the clinician may wish to compare different responses to treatment of similar conditions in a number of patients. As in the case of assessment of a single patient during treatment, a reliably consistent measurement of redness of the bulbus oculi or the tarsal area would assist the clinician in assessing the responses to treatment.
Known methods and devices for assessing the redness of an exposed portion of the bulbus oculi or an exposed portion of the tarsal area have not provided consistent measurements of redness. In general, redness is determined by the clinician visually comparing the redness of the exposed portion of the bulbus oculi or tarsal area, as the case may be, to reference color images. As indicated, colors other than red may be of interest, and in those circumstances, the reference color images would be of the color of interest. Typically, the reference color images are photographic representations of eyes with varying hues of red. Alternatively, the reference color images can be verbal (written) descriptions of various hues of red. The clinician is to apply the reference color images by visually comparing the redness of the exposed portion of the photographic or written reference color images, as the case may be. This method of determining redness is very approximate and unreliable. Because white light comprises an equal mixture of the primary colors, i.e., red, green, and blue, this known practice is, in effect, a crude estimate of the extent to which a particular primary color is reflected by the exposed portion being examined.
Other ways of assessing redness have been proposed, to provide more consistent assessment. For example, in P. Fieguth and T. Simpson, “Automated Measurement of Bulbar Redness”, Investigative Ophthalmology and Vision Science, February 2002, Vol. 43, Part 2, pages 340-7, a method of evaluating redness is disclosed in which an image of an exposed portion of the bulbus oculi of a subject was analyzed using numeric processing of pixels in the image by a computer to determine the extent of redness. The process was repeated with various subjects. The images were derived from photographs, however, with the result that some loss or distortion of relevant color information, when the image is captured and prepared for the numeric processing, is possible.
As noted, although the extent of redness is of interest, other colors may also be of interest to the clinician. Various other devices and methods are known for evaluating a particular condition of the bulbus oculi. However, these known devices and methods are not directed to measurement of the extent of redness (or any other color) of an exposed portion of the bulbus oculi or the tarsal area, as the case may be. For example, in U.S. Pat. No. 4,900,145 (Akiyama), an apparatus is disclosed which includes a laser beam projector. A laser beam sent from the projector scans a region inside the patient's bulbus oculi, to provide data for an evaluation of the concentration of protein in the anterior chamber of the eye. The invention disclosed in Akiyama is not directed to determining the color of the surface of an exposed portion of the bulbus oculi.
There is therefore a need for an apparatus and a method for measuring a hue of a predetermined primary color in light reflected from a surface.